Clonal crops are usually characterized during field regeneration. See also the regeneration page for the complete details of cultural practices.

Field planting for characterization and evaluation in the cassava genebank at CIAT (photo: C. Hershey)

Environment

Material should be characterized in an environment that is highly suited to cassava growth and development, and where biological and environmental problems are minimized, so that there are no confounding effects on the expression of traits used for characterization.

Normally unreplicated entries with control varieties regularly replicated (replication of only control varieties is sufficient for normal assessment of highly heritable morpho-agronomic traits; this practice is more economical and thus allows the screening of more accessions).

For special-purpose characterization for more rigorous statistical analysis, full replication is necessary.

Standard check cultivars

Local standard cultivars should be used as a reference, especially for pest and disease screening.

The list of suggested descriptors below is from Fukuda et al. (2010), who developed a descriptor list for IITA. This is based on descriptors used by both CIAT (Colombia) and EMBRAPA (Brazil), and thus encompasses the world’s major cassava collections. The publication includes a full complement of colour photos to facilitate understanding of the states of each descriptor.

In addition to the above, any other local quality traits of importance could be included. New traits identified by industry should be considered for inclusion, such as the ratio of amylose to amylopectin.

Pictures for characterization

Sufficient detail should be captured in images to taxonomically identify the plant and demonstrate the traits that show variation.

Take images for character(s) which may be difficult to describe verbally.

Store in a database file linked to other characterization data.

Herbarium samples for characterization

It is suggested they should be taken and stored for future reference during multiplication/regeneration, particularly for primitive and wild relatives (to verify the accession identity and to be used as reference material).

Molecular descriptors for characterization

SSR, EST-SSR, AFLP, RAPD (these are the current more efficient techniques for genetic diversity analysis and to identify duplicates).

Cytological characterization

This type of characterization should be done in specialized laboratories. Cytological characterization, with current available techniques, is not likely to be broadly applied across all accessions of a collection, but might be targeted to sub-samples such as the core collection.